1. Field of the Invention
The present invention relates to a heat exchanger for thermal conditioning of one fluid medium by heat transfer with a second fluid medium in a heat transfer tube and, more particularly, to a heat exchanger construction to provide inner and outer flow spaces for a two stage heat transfer with a fluid medium also passed consecutively along the flow spaces.
2. Description of the Prior Art
Evaporator and condenser functions provided by a heat exchanger are commonly used for diverse applications and while not so limited, the present invention is particularly useful in one common field of used where heat transfer with one medium consists of a flow of water for a swimming pool or spa. Swimming pool water is heated or cooled depending on the climate affecting the temperature of the pool water. The present invention is particularly applicable to a heat exchanger using a tube-in-shell construction. It is known to heat a flow of water for a swimming pool in an elongated tank having an internal chamber in which an electrically resistive heating element, frequently as a coil, is housed. Water is directed in a lengthwise path through the tank chamber containing the heating element for transfer of heat from the heating element to the water. In such a device, no control over the flow of water is provided within the internal chamber of the tank and because the heat exchanger incorporates an electrically resistive heating element as opposed to a fluid heat transfer medium, the application of such a heat exchanger is limited to use as a heater for water.
It is well known in the art to provide a heat exchanger to condition a flow of water in which a fluid is used as a heat transfer medium. In a type of construction known as xe2x80x9cshell-and-tubexe2x80x9d design, the heat transfer fluid is carried within a tube and the flow of water to be treated is directed past the tube, or tubes, within a shell housing. In the simplest arrangement, the heat exchanger consists of a tube within a tube and the fluids move either in the same direction, known as a xe2x80x9cparallel flowxe2x80x9d heat exchanger, or in opposite direction, known as a xe2x80x9ccounter flowxe2x80x9d heat exchanger. In a tube within a tube construction, the outer shell provides the outer boundary to the water passageway along the shell which is the only control over the flow of water once it has entered the shell. The heat exchange coils spaced inwardly from the sidewall of the shell enhances turbulence, thus also assisting in the desired heat transfer. Typical designs allow a large percentage of water entering the shell to pass through without coming in contact with the heat exchange coils. Also the tube in shell design typically uses plastic for the shell material and glued to construction prevents easy of disassembly for servicing of the heat exchanger. Such a construction, although embodying a simple arrangement of parts, is costly as to fabrication. These disadvantages are also present in other shell-and-tube heat exchanges having a shell to house multiple tubes or a coiled tube.
In U.S. Pat. No. 6,293,335, there is disclosed a tube and shell heat exchanger having a transversely oriented inlet port and a spirally coiled heat transfer tube contained within an arcuate chamber created by an internal baffle in which the water to be conditioned travels along a helical pathway in which the flow has minimized water depth and high turbulence. This water flow management design imposed a large water pressure drop along the path of travel along the arcuate chamber containing the heat transfer tube. Compared to our earlier submission, already patented, which had a high-pressure drop on the waterside. The tube and shell heat exchanger maximizes heat transfer capability in a relatively easy to assemble design to make feasible the use of a higher cost material for the tubing such as titanium in a wide range of applications. The heat transfer tube is commonly formed from a metal such as copper or copper-nickel alloy to take advantage of favorable heat transfer properties and low cost of the metal material. Because of the favorable heat transfer properties with metals as copper and copper-nickel alloy, when heating an increased water flow is necessary the requirement is met by increasing the length of copper tubing in the coiled section thereby providing a greater residence time for the water flow in the heat exchanger. Where higher BTU heat transfer is needed for a given flow of water through the shell, providing a greater length of tubing to achieve the desired BTU heat transfer is conventional and cost effective rather than direct or otherwise manage the water flow to maximize heat transfer. Increasing the size of the heat exchanger to achieve the desired BTU heat transfer imposes a penalty of a disproportionate heat loss from the increase surface area of the housing needed to accommodate the additional length of tubing.
There are disadvantages associated with a copper heat transfer tube in a heat exchanger for water. One example of such disadvantages is in the thermal conditioning of salt water for applications such as holding tanks and aquariums for marine life. The marine life is susceptible to a toxic reaction to chemically produce products of corrosive reaction between the salt water and the copper metal of the heat transfer tube. The toxic reacting product can be eliminated by selecting a more chemically inert metal or alloy such as titanium to form the heat transfer tube in the heat exchanger. The use of titanium for the heat transfer tube of the heat exchanger offers the benefits of strength, durability and a prolonged service life as compared with copper for the heat transfer tube of a heat exchanger. However, to be economically competitive the high cost of titanium metals as compared with the cost of copper or copper-nickel alloy poses a need to maximize the heat transfer in a minimized heat transfer space and minimize thermal losses to the atmosphere.
Accordingly, it is an object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium within a shell along inner and outer heat exchange cavities each containing a helical conduct convolutions to maximize heat transfer between a fluid medium and heat transfer conduct.
It is another object of the present invention to provide complete control to the path of water flow through a coil in a tube in shell type heat exchanger to insure that all water flowing through the shell comes in contact or into such close proximity with the coil for enhanced heat transfer in the path of the water flow.
It is still a further object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium in which the flow of the fluid medium within a shell is reversed for between consecutive annular passageways one contained within the other and inner connected for continuous flow within a heat exchanger housing to minimize thermal losses to the atmosphere and to maximize heat transfer efficiency.
According to the present invention there is provided a heat exchanger to thermally condition a fluid medium, the heat exchanger including the combination of a shell having an outer shell sidewall spaced from an internal shell sidewall both closed in a fluid tight manner by a first end wall for defining an outer heat exchange cavity and an inner heat exchange cavity, a second end wall joined with the outer shell sidewall in a fluid tight manner and spaced from the internal shell sidewall to form a fluid pervious flow space interconnecting the outer heat exchange cavity and the inner heat exchange cavity, shell conduits forming an inlet port and an outlet port for conducting a flow of a first fluid medium along each of the outer heat exchange cavity and the inner heat exchange cavity, an elongated tubular conduit permeating the shell in a fluid tight manner and having a tubular conduit portion traversing the internal shell sidewall between outer helical conduit convolutions resident in the outer heat exchange cavity and inner helical conduit convolutions resident the inner heat exchange cavity for conducting a second fluid medium in a heat transfer relation with the first fluid medium, and a flow controller supported by the second end wall and having a media dispersing wall forming an inner boundary to the inner heat exchange cavity for directing a flow of the first fluid medium along the inner heat exchange cavity.